In the related art, as a method for achieving high output of a laser, a method of multiplexing a plurality of laser lights from a plurality of light sources to one optical fiber or the like (JP-A-2002-202442) and a method of bundling fibers to which a plurality of light sources are coupled and coupling them to a single fiber are known.
However, in the case of multiplexing to a single optical fiber having a value which is equal to or several times the value obtained by multiplying emitter sizes and beam divergence angles of a plurality of independent package type semiconductor lasers, it is not easy to efficiently couple a plurality of laser lights to a fiber having a core of such a size as to be difficult to align the laser lights therewith. Further, in such a case, since the plurality of laser lights are incident on a cladding and a cladding mode light propagates through the cladding, it is necessary to absorb the cladding mode light.